There are switching regulator power supply devices for acquiring an insulated output voltage, wherein two secondary windings are provided in an insulating transformer, to thereby produce a non-insulated output voltage by voltage feedback using one of the two windings on the non-insulated side, and providing an insulated output voltage using the other of the two windings on the non-insulated side. In such power supply devices, an input current is detected, which flows through primary windings of the transformer. Compensation is provided by control of a switching element using the detected current value. Such power supply devices can have fluctuations in the output voltage value due to load fluctuations on the insulated side of the power supply, and become unstable as a result of changes in the power supply voltage.